Method of and apparatus for pumping liquefied gases



Dec. 22, 1953 c. R. ANDERSON ,66

METHOD OF AND APPARATUS FOR PUMPING LIQUEF'IED GASES Filed Aug. 22, 1949 2 Sheets-Sheet l INVENTOR N ,CABL R. ANDERSON ATTORNEY Dec. 22, 1953 c. R. ANDERSON METHOD OF AND APPARATUS FOR PUMPING LIQUEFIED GASES 2 Sheets-Sheet 2 Filed Aug. 22, 1949 INVENTOR CARL R. ANDERSON ATTORNEY Patented Dec. 22, 1953 UNITED STATES PATENT other:

Carl R. Andersom-Allentown, Pal, assignor to Products, Incorporated; a corporation of Michigan This invention relates to a method. andzaps paratus for pumping liquefied gaSES 'fIOIIPcEL gas separation operation. This application is a continuation-in+part of my copending applications Serial'No; 488,650; filed May27, 1943, issuing as Patent No. 2,480;093 and Serial No. 605,407, filed July 16, 1945; issuing as Patent No. 2,480,094:

An important object of the invention is f to provide a method and means forpuinp'ingia liquefied gas product from a fractionating operation utilizing colder fluids from the fracftionating operation toprevent gas lock: in ith'e pumping step. I

Another important obj'ect i of" the invention is to provide a method and means forpumping a stream of liquefied gas product of a fi-aetionatin'g' operation utilizing a cold liq'uidfromthe Trac tionating operationto cool the pump.

A further important objector the invention is to provide a method and means for pumping liquefied oxygen directly from a pool of"com-' mercially pure oxygen in afractionating tower to cylinders or pipe lines in which a cold gas is utilized to subcool the liquefied oxygen on the way to the pumping step and a relatively cold liquid from the fractionating operation is used to cool the pump.

A further important object of the invention is to provide a method and means for pumping natural gas in liquid phase from a fractionating system wherein it has been separatedfrom its nitrogen content to cylinders or pipe lines'in which it is transported under a high'pressure, thereby avoiding the necessity for a gaseous compressing system.

While the invention is applicable 'to the handling of all liquefied gases (liquids having a' boiling point so much below atmospheric temperature that heat leaking into insulated a para tus is likely to produce difiiculties in pumping), it is found most useful in connectionwiththe pumping of liquid oxygen because of the very low atmospheric pressure boiling point of this liquid. The invention will, therefore, be described in connection with the manipulation of oxygemit'being understood that such description is illustrative and not limiting.

If the oxygen product obtained in air frac tionation were to be recovered as a gas at atmospheric temperature and pressure, it would merely be conducted in gaseous form to aninter'changer, the pressure in the column being sufiicientto discharge the gaseous product against frictional resistance and atmospheric pressure. it is, how

i 2 everfverydesirable inmany cases to conduct the oxygenproduct directly to the cylinder or pipe lines'inv which itis transported asa compressed gasy'at pressures ranging up to2509 or more pounds per squareinch'. Although it is common practice to bringthe gaseous oxygen to substantiallyatmospheric temperature and pressure and to thereafter compress it, it isdes'irable to pump it as-a liquid andto vaporize it while subjected to theraisedpressure, prior to entering the pipe line or storage vessel H An advantagein.pumping'rthe oxygen in liquid phase lies in the avoidance of use of the aqueous lubricants required in compressing oxygen, these lubricants introducing water vapor which must be removedby chemicaldrying and adsorption to'obtain dry oxygen in the transport cylinders or-pipeline. r v V p The step, of pumping liquid oxygen has proven in practice to be one of great difficulty. The liquid is, in the; nature of the case, at its boiling point at theexisting pressure. From this, it follows that any reduction in'pressure, such as is cccasioriled by'fluid friction in t he pump suction, or anyincrease in; enthalpy due to leakage into the-pump bod or to vfrictionalheat'transmitted into theliquid, will [cause the evolutionpi gas whichlocks -the' suction puts 'thepum'pput 7 ofcommission}; A further cause of vapor lock is back leakage thro'ughLthe discharge valve, the high pressure leakage liquid partially flashing to the-gaseousstate.

I havesolved this problem by two steps which are preferably useditogether'but may-i be used individually. 'f helfirst' is to utilize a small portionof 'thewcooling' .effect available in a colder fluid 'from the fractionating operation forcooling the'streamof liquid-oxygen, on its way to the-pump, to a temperature below that correspondingito its boilingpointat the pressure e istinginthe pump cylinder during the suction StlOkBs: The second is to utilize a portion of the refrigerating value of a cold-liquid from the fracti'onatingfoperation in cooling the pump cylinder. In the attached drawings-the inventionis illustrated schematically in two modifications; to wit: l r p Figure 1 illustrates aform in which oxygen in the liquidstate is pumped from the pure oxygen pool of a single;fractionating column' and the stream is cooled below its boiling point at the pressure-existing in thepump cylinder duringthe --suction' stroke by heat exchange against gaseous product nitrogen from the; topofthe columm and in which the pump cylinder is cooled .used for conducting the liquefied feed by heat exchange against the liquefied air feed stream.

Figure 2 illustrates a form in which oxygen is withdrawn in the liquid state from the pure oxygen pool in the base of the lower pressure section of a double iractionating column and is cooled below its boiling point at the pressure ex isting in the pump cylinder during the suction stroke by heat exchange against gaseous product nitrogen from the low pressure stage of the column, and in which the pump cylinder is cooled by heat interchange with expanded crude oxygen in its passage from the high pressure to the low pressure stage of the column.

The iractionating equipment illustrated is conventional, and any preferred form of either single or double fractionating column may be used.

Referring to the drawings, the system shown in Fig. 1 includes a heat interchanger A having two banks of tubes II, II and l2, l2 within an outer shell 13 to provide three passageways therethrough in heat exchange relationship with one another. A single stage fractionating column B is provided with a plurality of bubbling plates [4 and a boiling coil IS in the base thereof. Compressed air enters the interchanger A through feed pipe 15, passes through tubes H, H and then through conduit H to the boiling coil i5 submerged in a pool of boiling oxygen H3 in the base of the column. The feed air is liquefied therein by giving up heat to the boiling liquid in the pool 53. The liquefied stream flows through conduit l9 and expansion valve 29 wherein it is expanded to the pressure existing in the fractionating column B. The expanded liquid air stream then flows to the coil 2i wrapped in heat exchange relationship around the cylinder of the pump C. In flowing through the coil 21, the liquid air stream prevents rise in temperature of the liquid in the pump to a point at which vapor would be evolved in the cylinder and tends to maintain the low temperature imparted to the liquid in a prior subcooling step to be described. From the coil 2i, the air flows through conduit 22 to the top of the column. In place of the coil 2|, a cooling jacket could be air stream in heat exchange with the pump cylinder. 7

Flowing downwardly through the column, the feed air is fractionated in the well-known man ner into a pure liquid oxygen product collecting in the pool 18 at the base of the column and into an impure gaseous nitrogen leaving the top of the column through conduit 23. Conduit 23 conducts the nitrogen product from the top of the column to a passageway through a heat interchanger 24 which surrounds a coil therein. Conduit 2E conducts the nitrogen from this passageway to the shell of interchanger A from whence it is vented through conduit 21. In flowing through the passageway of interchanger 24, the gaseous nitrogen stream is in heat exchange relation with coil 25.

The pure oxygen collecting in the pool l8, by nature of the operation at its boiling point, is removed from the column in liquid form through conduit 28 and flows through coil 25 of heat interchanger 24. Coil 25, as previously described, is in heat exchange relation with the gaseous nitrogen flowing in the space surrounding it, and the liquid oxygen flowing through the coil 25 is cooled therein to a temperature sufliciently below its boiling point so that there will be substantially no flashing of the oxygen into vapor under the pressures encountered in the subsequent pumping operation. The subcooled stream of oxygen flows through conduit 28 to the oxygen @pump C.

The oxygen pump indicated generally by the letter C may be any pump capable of handling liquids at high pressures but is here illustrated as a single acting plunger pump having a suction valve 36, a discharge valve 31, a cylinder 32, a plunger 33, a rod 34, a cross head 35, a connecting rod 36,a crank 31a driven gear 38,a drivingworxn gear 39 and an actuating motor ac. The subcooled stream of oxygen flows through conduit 29 and suction valve 30 into the pump cylinder on the upstroke of the plunger 33. On the down stroke, the liquid passes through discharge valve 3| and conduit 4| to the interchanger I0 flowing through the tubes l2 in which the stream is brought to atmospheric temperature and gaseous condition. The gas is discharged at any desired pressure through conduit 42. If desired, the stream in conduit 4! could be directed to a storage vessel in the liquid condition but usually it will be passed through the interchanger it and delivered by conduit 42 to pressure cylinders 43 or other pressure vessels or to pipe lines in which it is transported under pressure.

By the use of this cooling cycle, a properly designed and insulated pump may be caused to operate at full stroke capacity for extended periods and without any risk whatever of gas looking. The refrigerative value lost by the nitrogen in cooling the liquid oxygen is largely recovered in the evaporation of the oxygen in the interchanger. The heat absorbed by the liquefied feed air from the pump, which is due mainly to heat leakage from the atmospheric and packing friction, causes a small loss of refrigerating effeet which may be compensated by a correspondingly slight increase in air feed pressure.

In the form of the invention shown in Figure 2, heat interchanger A is provided with two banks of tubes 54, it and .5, 45 within an outer shell 3% to provide three passageways therethrough in heat exchange relationship. The fractionating column, indicated generally by reference character B, consists of a high pressure section 4i and a low pressure section 48, each supplied with a stack of bubbling plates as separated by a partition 593 which includes the conventional downwardly draining condenser 53, the condensate from which drains into the high pressure section of the column ll. Compressed air enters the interchanger A through feed pipe 52, passes through tubes as, .4 and then through conduit 53 to boiling coil 54 submerged in a pool of boiling crude oxygen 55 in the base of the high pressure section. The air flows from the coil 54 through conduit 56 and expansion valve 5? into the high pressure section of the column at a medial height. In this section of the column, the feed air is fractionated into a substantially pure gaseous nitrogen rising into the condenser 5| which is immersed in a pool of boiling pure oxygen 58 collecting in the base of the low pressure section of the column. As the upper section of the column is maintained at a materially lower pressure than the lower section, the condenser acts as a reboiler for the pure ox gen surrounding it. As a result, the nitrogen rich gas rising in the condenser is liquefied, part falling into the pool 59 and part falling onto the top plate of the lower section Ail where it acts as reflux for the lower section. Liquefied nitrogen from pool 59 is transferred through conduit i353 and expansion valve 5| to the top of the upper section inwhich it acts as reflux. The crude oxygen product formed in; the high pressure sectionof the column collects in the pool 55 in the base of the column. s 1

7 As shown in this form of the invention, thecrucle oxygen collecting in the pool 55 maybe utilized after expansion to cool the-cylinderof the pump C before passing to the lower pressuresection of the column. This is accomplished by withdrawing the crude oxygen through conduit- 62 and passing it through interchanger $3; to be described hereinafter, and conduit i35"to-expan sion valve 65 and thencethrough thecoolingcoil Si surrounding the oxygen pump 01- From the cooling coil 6?, which has-the same purposes-and functions as coil 2| in Fig. '1, the-crude oxygen flow through conduit B3 into thelow-pressure section of the column at a medial height therein.

The high pressure nitrogen stream'andthe high pressure oxygen stream flowinginto the low pressure section of the column are-frac-- tionated in the well-l nown manner-to'substantially pure oxygen and a slightly impure nitrogen product. The nitrogen product in gaseous form is withdrawn through conduit 68 at the top of the low pressure section of the column and is conducted to a passageway through the interchanger l8 surrounding a, coil El therein where-it passes thereof and is removed in liquid form throughconduit i5 and passes through the coil ii ininterchanger lii wherein it is subcooled by heat interchange with the gaseous nitrogen stream flowing in the space surrounding the coil H in the interchanger it. The liquid oxygenflowing through the coil '15 is thuscooled to a tempera-- ture sufficiently low so'tha-t there will be substantially no flashingof the oxygen into vapor during the subsequent pumping operation.

From the interchanger W, the pure oxygen product flows through conduit F6 to the suction valve i? of the liquid oxygen pump C wherein the stream is pumped to the-desired-pressure. The oxygen pump'C may be any pump capable of handling a liquid at high pressure-butis here illustrated as a single acting plunger pump having a suction valve if, a discharge valve W, a cylinder '59, a plunger 8d, a rod 8!, a'crosshead 82, a, connecting rod 83, a crank-8 E, a drivengear 85, a driving worm gear 85 and an actuating mo tor 8'1. The subcooled stream. of oxygen flows through conduit 16 and suction valve i! into the pump cylinder on the'upstroke of the plunger Bii. During its flow into and from the pump cylinder, the stream of liquid oxygen is prevented from rising in temperature to a point at which vapor would evolve under the conditions present,

by the liquid flowing through the coil 5? surrounding the pump cylinder, aspreviously described with respect to coil 2!. stroke of the pump plunger, the liquid oxygen passes through the discharge valve is and flows through conduit 98 to the-tubes 45," 45 of interchanger A in which thestream is brought-to at On the down conduit 9|. If desired, the stream in conduit may be directed to a storage vessel or pipe line in liquid condition, but usually it will be passed through the interchanger and delivered by conduit 9| to the pressure'cylinders $2 or other pressure vessels or to pipe lines in which it is transported under pressure in a gaseous state. Here again, the refrigerative value lost by the nitrogen incooling the liquid oxygen is largely recovered inthe evaporation of the oxygen in the interchanger A. The heat absorbed by the crude oxy gen' in coolingthe pump cylinder, due mainly to.

packing'friction and infiltration from the atmosphere, causes a small loss of refrigerating effect which maybe compensated by corresponding.

adjustments in the air feed pressure.

Heat interchanger E53 through which product nitrogen passes on its way to the main interchanger A subcools the crude oxygen on its way from the high pressure stage to the low pressure stage. The useof such an interchanger is com ventional, its purpose being to subcool the crude oxygen so as to reduce as far as possible the amount of flashing taking place when the crude oxygen is expanded. This interchanger s3 can be omitted from applicants cycle without dele.-- teriously affecting the pump cooling operation.

The cycles disclosed in the present application and in the applications of whichthe present application is a continuation-in-part can be utilized in: handling any mixture of low boiling point gases where there is a tendency for vapor lock in the pump. An especially useful application of these cycles is in the treatment of natural gas to.

remove liquefied petroleum gas fractions such as ethane, propane, butane, etc., normally referred to as. L. P. G. Even so-called dry natural gaswhen subjected to a refrigeration cycle and fractionation, will produce appreciable quantities of L. P..G. Natural gas is also treated by refrigeration and fractionation to remove nitrogen. The nitrogen in natural gas is a diluent.

which raises the cost of transporting the gas in pipe lines. In either case, the natural gas'is taken from the well for treatment, either at the. formation pressure, when it is high enough or,. if not, the gas is subjected to compreession. The.

gas under compression is cooled and expanded and the efiiuent subjected to fractionation to remove the nitrogen as overhead in one case and to remove the L. P. G. as bottom product in the other case.

The cycle of the present invention is readilyv adaptable to the foregoing treatment of natural gas. Natural gas under formation pressure or from compressors enters the system through i5, is cooled in heat interchanger A and passes, as has been described in the case of the air, through the remainder of the system. The bottom product corresponding to the pure oxygen is taken on in liquid form andits pressure raised to the desired storage or transportation pressure by pumping it in pump C in liquid phase. In the case where the bottoms are natural gas, with'or without L. P. G. as constituents, the pressure on the liquid product is raised in pump C to above pipe line pressure which in some instances may be as high or higher than 1000 pounds per square inch. The liquid under this pressure passes from pump C through heat interchanger A, giving up its cold to the incoming natural gas and nitrogen andat the same time being vaporized.

- Utilizationof the present system for handlingnatural gas results in great savings in compressor equipment where the pressure in the fractionating operation is appreciably below the pipe line pressure.

Where the recovery of L. P. G. from natural gas is to be effected utilizing the present inventreatment of air, fluids from the fractionator colder than the liquid product being pumped are used to prevent vapor lock of the pump.

1 claim:

1. In combination with a fractionating apparatus for separating a mixture of low boiling point gases, a pump adapted to handle liquids, a conduit connecting the suction of the pump with a relatively Warm liquid product collecting space in the apparatus, a heat interchanger interposed in the conduit, means for conducting a stream of a. relatively cold fluid from the apparatus through the interchanger in heat exchange elation with the relativay warm liquid product for forming a su'ocooled liquid product flowing toward the pump, heat transfer means associated with the liquid-conveying end of the pump, means for passing a second relatively cold fluid in liquid form from the apparatus through the said heat transfer means, and means for conducting second relatively cold fluid "from the 1.

heat transfer means to the apparatus.

2. In combination with an apparatus producing liquid oxygen product and a gaseous nitrogen-rich product, a liquid oxygen pump, means for bringing a stream of fluid from the liquid oxygen product from the apparatus into heat interchange relation with a fluid from the apparatus colder than the oxygen and thereby cool ing the oxygen stream, means for conveying the cooled oxygen stream to the pump, means for producing heat interchange between the pump and a second relatively cold fluid in liquid form from the apparatus, and means for returning second relatively cold fluid from the heat interchange With the pump to the apparatus.

3. In combination with a fractionating column wherein a compressed and cooled mixture of low boiling gases is fractionated thereby producing a liquid higher boiling fraction as a product, a pump adapted to the pumping of liquids, a conduit connecting the pump with the liquid higher boiling fraction collecting space in the column, heat transfer means in heat transfer relation with the liquid-conveying end of the pump, means for passing a fluid colder than the liquid higher boiling fraction in liquid form from the column through the said heat transfer means, and means for returning last-named liquid from the heat transfer means to the column.

i. In combination with a fraetionating column wherein a compressed and cooled mixture of low boiling gases is fractionated thereby producing a liquid higher boiling fraction as a product, a pump adapted to the pumping of liquids, a conduit connecting the suction of the pump with the liquid higher boiling fraction collecting space in the column, heat transfer means associated with the liquid conveying end of the pump, means for passing a stream of expanded liquefled feed mixture through the said heat transfer In fractionator B, the

- liquid oxygen flowing 8 means, and means for conducting feed mixture from the heat transfer means to the column.

5. In combination'with an air fractionatin column in which compressed and cooled air is fractionated in two stages maintained respectively at a relatively high and a relatively low pressure, in which a product enriched in nitrogen and a product enriched in oxygen are produced in the high pressure stage and transferred to the low pressure stage and in which a cold nitrogen product and a liquid oxygen product having a temperature corresponding to its boiling point at the low pressure are produced in the low pressure stage, a pump adapted to the pumping of liquids, a conduit connecting the suction of the pump with the liquid oxygen collecting space in the low pressure stage of the column, heat transfer means in heat exchange relation with the liquid conveying end of the pump, means for passing expanded liquid product enriched in oxygen from the high pressure stage of the column through the said heat transfer means and, means for conducting liquid product enriched in oxygen from the heat transfer means into the low pressure stage of the column.

6. In combination with an air iractionating column in which compressed and cooled air is fractionated in two stages maintained respectively at a relatively high and a relatively low pressure, in which a product enriched in nitrogen and a product enriched in oxygen are produced in the high pressure stage and transferred to the low pressure stage and in which a gaseous nitrogen product and a liquid oxygen product having a temperature corresponding to its boiling point at the low pressure are produced in the low pressure stage, a pump adapted to the pumping of liquids, a conduit connecting the suction of the pump with the liquid oxygen collecting space in the low pressure stage of the column, a heat interchanger interposed in the conduit, means for directing a stream of fluid from the column colder than the liquid oxygen through the interchanger in heat exchange relation with the through the conduit toward the pump, heat transfer means associated with the liquid conveying end of the pump, means for passing expanded liquid product enriched in oxygen from the high pressure stage of the column through the said heat transfer means and means for conducting product enriched in oxygen from the heat transfer means into the low pressure stage of the column.

7. In combination with a fractionating column wherein a compressed and cooled mixture of low boiling gases is fractionated thereby producing a liquid higher boiling fraction and a gaseous lower boiling fraction as products, a pump adapted to the pumping of liquids, a conduit connecting the suction of the pump with the liq id higher boiling fraction collecting space in the column, a heat inter-changer interposed in the conduit, means for directing a stream of relatively cold fluid from the column through the interchanger in heat exchange relation with the liquid higherboiling fraction flowing through the conduit toward the pump, heat transfer means associated with the liquid conveying end of the pump, means for passing a stream of expanded liquefied feed mixture through the said heat transfer means, and means for conducting expanded liquefied feed mixture from the heat transfer means to the column.

8. The method which comprises withdrawing a stream of higher boiling fraction from a fractionating operation inwhich a mixture of low boilinggasesiis'fseparated into a liquid higher lboiling fraction product and a gaseous lower ond fluid stream from the fractionating operaj tion in liquid phase, expanding the second fluid stream to a pressure such that the expanded secnd fluid stream has a temperature-below the boiling point of the liquid higher boiling fraction at the minimum momentary pressureureached in the pumping step, maintaining the liquid higher boiling fraction being pumped below its boiling point during the" pumping step by effecting -a heat interchange between the pump and a stream of expanded second fluid in liquid phase,

and passing expanded second fluid from the heat interchange with the pump to the fractionating operation. 7

9. The method --which comprises withdrawing a stream of liquid product at its boiling temperature from a collecting zone in a 'fractionating operation in which amixture of low boiling gases is separated into a liquid product and a gaseous product, efiecting a heat interchange between the stream of liquid product and a cold fluid stream from the fractionating operation-which is colder than the stream of liquid product to reduce the temperature of the liquid product to a pointbelowthe boiling point of the liquid product at :the minimum momentarypressure reached in an ensuingpumping step, pumping the cooled stream of liquid product in substantially liquid form, withdrawing a secondfluid stream from the fractionating'operation in liquid phase, expanding the second fluid stream to a pressure such that the'expanded fluid stream has a temperature'below' the boiling point of the liquid product'at the minimum momentary pressure reached in the pumping step, 'maintaining the liquid product'being pumped below its .looil- 'ing point during the pumping step by effecting a heat interchange between Lthe'pump and, a

stream of expanded second fluid in liquid phase, and passing expanded second fluid from the heat interchange with the pumpto the fractionating' operation.

10. In'a method wherein a compressed, and cooled mixture of low boiling gases isfra'ction ated in an operation producing liquid and gaseous products, the steps comprising subjecting a'relatively warm liquid product of the fractionation to heatexchange with a colder fluid from the fractionaticnto reduce the temperature of theliquidproductv to a point below the boiling point of the liquid :product at the minimum.

momentary pressure .reached in an ensuing pumping step and thereby forming asufocooled liquid. product, pumping such subcooled liquid product to a desired higher pressure, withdrawing a second fluid stream from the operation in I liquid phase, expanding thefsecond fluid stream to a pressure such that the expanded fluid stream has a temperature belowthe boiling point of, the liquid product at the minimum momentary] pressure reached in the pumping step, maintaining the liquid product being pumped belowitsj'boiling point during the pumping step by subjecting the pump to heat exchange with a stream of expanded second fluid in liquid phase, passing expanded second fluid fromithe heat exchange with the pump to the "operation, and converting the pumped liquid product at the higher pressure into a gas by heat exchange with the compressed mixture to be fractionated.

I 11. In the conductof a multistage fractionating operation, the steps comprising, withdrawing a stream of 1the'higher boiling fraction from the lowpressure stage of the operation, bringing the 'colder iiuid stream from the fractionating operastream' into heat interchange against another 'tion to reduce'the temperature of the higher boil- "ingfrraction to a pointbelow the boiling'point jof the higher boiling fraction at the minimum momentary pressure reached in an ensuing pumping step, pumping the cooled higher boiling' fraction in substantially liquid form, withdrawing a second fluid stream from the fraction- "ating operation in liquid phase, expanding the second fluid stream to a pressure such that the expanded 'fluid stream has a temperature below the boiling point of the higher boiling fraction at the minimum momentary pressure reached in [the pumping step, maintaining the'higher boiling fraction being pumped below its boiling point during the pumping step by eiTecting a heat interchange'between the pump and a stream of expaneled second fluid in liquid phase, and passing fexpanded second fluid from the heat interchange with the pump to the fractionating operation. 1 2.,In' a method wherein a compressed and cooled'mixtur of low boilinggases is fractionated j in anoperation producingliquid higher boiling fraction andgaseous "lower boiling fraction as products, the steps comprising withdrawing a stream of the higher boiling fraction product from the fractionating operation, pumping the stream of .higher boiling fraction product in substantially liquid form, expanding a stream .of

liduidfeedunixture to be fractionated to a pressure such that the expanded feed mixture has a temperature below the boiling point of th liquid higher boiling fraction at the minimum momentary pressure reached in the pumping step,

maintaining the liquid higher boiling fraction be- .i ng pumped below its boiling point during the pumping step by. efiecting a heat interchange between th pump and a stream of expanded liquid feed mixture, and passing expanded feed mixture from .therheat interchange with the pump to .the

. operation.

.13. In a method .wherein a compressed and cooled mixture of low boiling gases, is fractionated in an operation producing liquid higher boiling fraction and gaseous lower boiling fraction as products, thesteps comprising withdrawing a stream of the higher boiling fraction product from the fractionating operation, subjecting the stream' of higher boiling fraction to heat exchange with a. colder fluid from the fractionating operation to reduce the temperature, of the higher boiling fraction to apointbelow the boiling point of the' higher boiling fraction at the minimum momentary pressure reached in an ensuing pumping stepand thereby forming a subcooled liquid .higher boiling fraction stream, pumping the subcooled liquid higher boiling fraction stream to a'desiredhigher pressure, expanding a streamof liquidfeedmixture to be fractionated to a pressure suchthat the expanded feed mixture has a temperature below the boiling point of the liquid higher boiling fraction at the minimum momentary pressure reached in the pumping step, maintaining the liquid higher boiling fraction being pumped below its boiling point during the pumping step by effecting a heat interchange between the pump and a stream of expanded liquid feed mixture, and passing expanded liquid feed mixture from the heat interchange with the pump to the operation.

14. In a method for producing oxygen and conditioning it for delivery to a receiving means. in which compressed and cooled air is rectified in two stages maintained respectively at a relatively high and a relatively low pressure, in which a product enriched in nitrogen and a productenriched in oxygen are produced in the high pressure stage and transferred to the low pressure stage and in which a cold nitrogen product and a li uid oxy en ro u t hav n a tempe ature corresponding to its boiling point at the low pressure are produced in the low pressure stage, the steps comprising withdrawing a stream of the liquid oxygen product from the low pressure stage of the column, pumping the oxygen stream in substantially liquid form, withdrawing a stream of liquid product enriched in oxygen from the high pressure stage, expanding the stream of liquid product enriched in oxygen to a pressure such that the expanded liquid product enriched in oxygen has a temperature below the boiling point of the liquid oxygen product at the minimum momentary pressure reached in the pumping step, maintaining the li uid oxygen product being pumped below its boiling point during the pumping step by passing a stream of expanded liquid product enriched in oxygen in heat interchange with the pump, and passing product enriched in oxygen from heat exchange with the pump into the low pressure stage.

15. In a method for producing oxy en and conditioning it for delivery to a receiving means, in which compressed and cooled air is fractionated in an operation including two stages maintained respectively at a relatively high and a relatively low pressure, in which a product enriched in nitro en and a liquid product enriched in oxygen are produced in the high pressure stage and transferred to the low pressure stage and in which a cold nitrogen product and a liquid oxygen product having a tem erature corresponding to its boiling point at the low pressure are produced in the low pressure stage, the steps comprising withdrawing a stream of the liquid oxygen product from the low pressure stage, effecting a heat interchange between the oxygen stream and another cold fluid stream from the fractionating operation which is colder than the oxygen stream to reduce the temperature of the oxygen stream to a point below the boiling point of the liquid oxygen product at the minimum momentary pressure reached in an ensuing pumping step, pumping the cooled oxygen stream in substantially liquid form, withdrawing a stream of liquid product enriched in oxygen from the high pressure stage, expanding the stream of liquid product enriched in oxygen to a pressure such that the expanded liquid product enriched in oxygen has a temperature below the boiling point of the liquid oxygen product at the minimum momentary pressure reached in the pumping ste maintaining the liquid oxy e product being pumped below its boiling point during the pumping tep y effecting a heat mter" change between the pump and a St ea f panded liquid product enriched in oxygen, and passing expanded liquid product enriched in oxygen from the heat interchange with the pump into the low pressure stage.

16. The method of transferring the liquefied rcduct obtained in the treatment of natural gas to reduce its nitrogen content, in which treatment a compressed and cooled nitrogen-containing natural gas is expanded and the efiluent of the expansion step subjected to a iracti'onating operation to produce a liquefied natural gas fraction and a gaseous nitrogen fraction, comprising withdrawing a stream or the liquefied natural gas fraction from the iractionating operation, pumping the stream of liquefied natural gas fraction in substantially liquid form, and maintaining the liquefied natural gas fraction being pumped below its boiling point during the pumping step by passing a relatively cold fluid stream from the fractionating operation in heat interchange with the pump, the relatively cold fluid stream being at atemperature below the boiling point of the liquefied natural gas fraction at the minimum momentary pressure reached in the pumping step.

17. The method of transferring the liquefied product obtained in the treatment of natural gas to reduce its nitrogen content, in which treatment a compressed and cooled nitrogen-containing natural gas is expanded and the eriluent of the expansion step subjected to a iractionating operation to produce a liquefied natural gas fraction and a gaseous nitrogen fraction, comprising withdrawing a stream of li uefied natural gas fraction from the fractionating operation, efiecting a heat interchange between the liquefied natural gas fraction stream and another cold fluid stream from the fracticnating operation which is colder than the liquefied natural gas fraction stream to reduce the temperature of the liquefied natural gas fraction stream to a point below the boiling point of the liquefied natural gas fraction at the minimum momentary pressure reached in an ensuing pumping step, pumping the cooled liquefied natural gas fraction stream in substantially liquid form, maintaining the liquefied natural gas fraction being pumped below its boiling point during the pumping step by effecting a heat interchange between the pump and a relatively cold fluid stream from the fractionating operation, the relatively cold fluid stream being at a temperature below the boiling point of the liquefied natural gas fraction at the minimum momentary pressure reached in the pumping step, and passing relatively cold fluid from the heat interchange with the pump to the iractionating operation.

18. The method of transferring the liquefied product obtained in the treatment of natural gas to reduce its nitrogen content, in which treatment a compressed and cooled nitrogen-contain ing natural gas is expanded and the efliuent oi the expansion step subjected to a iractionating operation to produce a liquefied natural gas fraction and a gaseous nitrogen fraction, comprising withdrawing a stream of liquefied natural gas fraction from the iractionating operation, efiecting a heat interchange between the lique" fied natural gas fraction stream and another cold fluid stream from the iractionating operation which is colder thanthe liquefied natural gas fraction stream to reduce the temperature or the liquefied natural gas fraction to a point below the boiling point of the liquefied natural gas fraction at the minimum momentary pressure cooled liquefied natural gas fraction stream in substantially liquid form, maintaining the liquefied natural gas fraction being pumped below its boiling point during thepumping step byeffecting a heat interchange between the pump and a relatively cold fluid stream from the fractionating operation in liquid phase, the relatively cold fluid stream being at a temperature below the boiling point of the liquefied natural gas fraction at the minimum momentary pressure reached in the pumping step, and passing relatively cold fluid from the heat interchange with the pump to the fractionating operation.

'19. In a method wherein a compressed and cooled mixture of low boiling gases i 'iractionated thereby producing a liquid product and a gaseous product, the steps comprising withdrawing a stream of the liquid product at its boiling temperature from a collecting zone in the fractionating operating; pumping the stream of liquid product in substantially liquid form, Withdrawing a second fluid stream from the fractionating operation in liquid phase, expanding the second fluid stream to a pressure such that the expanded second fluid stream has a temperature below the boiling point of the liquid product at the minimum momentary pressure reached in the pumping step, maintaining the liquid product being pumped below its boiling point during the pumping step by effecting a heat exchange be tween the pump and a stream of expanded second fluid in liquid phase, and passing expanded second fluid from the heat exchange with the pump to the fractionating operation.

20. In a method wherein a compressed and cooled mixture of low boiling gases is fractionated thereby producing a liquid product and a gaseous product, the steps comprising withdrawing a stream of the liquid product at its boiling temperature from a collecting zone in the fractionating operation, subjecting the stream of higher boiling fraction to heat exchange with a stream of the gaseous product to reduce the temperature of the liquid product to a point below the boiling point of the liquid product at the minimum momentary pressure reached in an ensuing pumping step and thereby forming a subcooled liquid product stream, pumping the subcooled liquid product stream to a desired higher pressure, expanding a stream of liquid feed mixture to be fractionated to a pressure such'that the'expanded feed mixture has a temperature be low the boiling point of the liquid product at the minimum momentary pressure reached in the pumping step, maintaining the liquid product being pumped below its boiling point during the pumpin step by eflectinga heat interchange between the pump and a stream of expanded liquid feed mixture, and passing expanded feed mixture from the heat interchange with the pump to the fractionating operation.

CARL R.'A'NDERSON.

References Cited in the file of this patent UNITED STATES PATENTS 

